seaweed

Seaweed being harvested for commercial use. Generally growing in shallow water, where sunlight is able to reach, seaweed is relatively easy to gather. The purple laver, dulse, brown gulfweed, and the green laver (or sea lettuce) are among the seaweeds harvested for food. Other varieties such as kelp are used in fertilizers, while Gelidium is used to make agar (a thickening agent used in the food industry).

Any of a vast group of simple multicellular plant forms belonging to the algae group, and found growing in the sea, brackish estuaries, and salt marshes, from near the high-tide mark to depths of 100–200 m/300–600 ft. Many seaweeds have holdfasts (attaching them to rocks or other surfaces), stalks, and fronds, sometimes with air bladders to keep them afloat, and are green, blue-green, red, or brown.

Worldwide there are approximately 2,000 species of brown macroalgae (Phaecophyceae), 5,500 reds (Rhodophyceae), and 1,200 greens (Chlorophyceae), most of which are marine. Some have traditionally been gathered for food, such as purple laver (Porphyra umbilicalis, which is used by the Japanese to make sushi), green laver (Ulva lactuca), and carragheen (Chondrus crispus). From the 1960s, seaweeds have been farmed, and the alginates (salts) that are extracted are used in convenience foods, ice cream, and animal feeds, as well as in toothpaste, soap, and the manufacture of iodine and glass.